Fluid working apparatus can broadly be broken into two basic types, namely, positive displacement and non-positive displacement. Positive displacement apparatus include reciprocating piston systems such as reciprocating piston engines, compressors, pumps, and the like. Positive displacement apparatus also include various rotating lobe engines and compressors. Non-positive displacement apparatus include turbine engines, centrifugal compressors, centrifugal pumps, and other equipment.
Positive displacement engines mechanically define the volume of the working fluid. This allows relatively high levels of torque to be developed over a broad range of operational speeds. Non-positive displacement engines such as turbine engines do not perform efficiently away from the design operational parameters. The loss of efficiency and power away from the design parameters renders them less effective where varying power, torque and speed requirements exist, such as for vehicular engines.
Reciprocating piston engines are currently in widespread use. Despite their reliable performance and broad torque capabilities, they suffer from a number of disadvantages. A principal problem of reciprocating piston engines is the relatively low speeds at which they must be operated. Low speed operation is necessitated by the relatively high accelerations experienced by the pistons and connecting rods as they start and stop twice during each rotation of the crankshaft.
Reciprocating engines also suffer from relatively high frictional losses. Principal sources of high friction are the piston rings or seals. Such ring seals are necessitated because of the relatively higher operating temperatures of the pistons in comparison to the cylinder walls which are usually cooled, such as by circulated water. Clearance must be provided between the pistons and cylinder walls so that the relatively greater thermal expansion of the pistons can be accommodated. Such clearances are sufficiently large that unsealed bypass leakage cannot be tolerated, thus requiring the sealing rings or some equivalent. Piston rings drag along the cylinder walls causing significant friction losses and necessitating almost constant lubrication of the seals and cylinder walls. Engine oils used in piston engines are thus exposed to the hot combustion gases which deteriorate the lubricating ability of the oil. This leads to increased maintenance in addition to the high frictional losses associated with the sealing rings.
Reciprocating piston engines are also plagued by geometrical and structural limitations which severely restrict the ability of the working fluid, such as air, to flow into and out of the combustion chamber. Typical reciprocating engine configurations use poppet type valves which have relatively small flow areas and convoluted flow paths. The associated valve lifting systems are relatively complex and utilize a large number of relatively costly components which also cause significant frictional losses. Such valve systems are also susceptible to deterioration as the combustion gases flow across the sealing surfaces of the valve.
Reciprocating piston engines are further characterized by exposure of the entire piston head to the hot combustion gases. This causes the piston head to be heated to such an extent that substantial cooling is required. This cooling increases engine cost and reduces engine efficiency.
Prior art inventions have addressed some of the limitations and disadvantages discussed above using rotary concepts. One of the most widely known alternatives is the Wankel rotary engine. Unfortunately, the Wankel engine suffers from a number of limitations, some of which are particular to that configuration. One of the most serious problems of the Wankel engine is the relatively short life of the apex seals located at the corners of the three-sided rotor.
The Wankel engine configuration is also disadvantageous because the high pressures of ignition and combustion are distributed over one full face of the three-sided rotor. This places substantial lateral forces on the rotor shaft which causes significant shaft deflection and further requires sealing the combustion chamber against leakage at the apexes of the rotor. High speed operation of Wankel engines further causes the rotor tips to move closer to the epitrochoidal chamber wall in which they operate. This further necessitates use of apex seals since clearance must be increased to allow operation up to the desired maximum engine speed.
The present invention provides a novel expandable and contractible fluid working apparatus well suited for use as an internal combustion engine. Other uses are also possible, such as for compressors, pumps, and in other fluid working applications.